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Orthopyroxene is an abundant mineral in subducting slabs. Studying its phase transitions at high pressure is important to the understanding of mineralogy of subducting slabs in the deep Earth. Synchrotron-based single-crystal X-ray diffraction experiments were conducted on a synthetic Ni-bearing ferrosilite (Ni-En31Fs65) at pressures up to 33.8 GPa. Three phase transitions were observed at 12.1(6), 15.6(6), and 31.3(25) GPa. The first two phase transitions in Ni-En31Fs65resemble the previously described phase transitions in Ni-free Fe-rich orthopyroxenes, i.e., the initial α-opx (Pbca) transforms to β-opx (P21/c), then the latter transforms to γ-opx (Pbca). This indicates that the incorporation of a few mol% NiSiO3does not influence the phase transition path of Fe-rich orthopyroxene. After the third phase transition, the structure (P21ca) of Ni-En31Fs65resembles the previously reported β-popx observed in En90at high pressure, although the onset pressure of the phase transition in Ni-En31Fs65is ~7 GPa lower than that in En90. β-popx has a post-pyroxene structure that contains fivefold- and sixfold-coordinated Si cations. Our results indicate that the post-pyroxene structure is β-popx (P21ca) for either Fe-poor or Fe-rich orthopyroxenes, although the phase transition path before the pyroxene → post-pyroxene is compositionally dependent. Additionally, unlike the second and third transitions, whose onset pressures are monotonously decreased by increasing Fe content, the Fe effect on shifting the first transition is much more significant for orthopyroxenes within En <50 mol% than that within En >50 mol%.

Understanding the structural evolution of carbonate minerals with increasing pressure is essential to decoding the role of Earth’s mantle in the global carbon cycle and long-term climate change. Here, we carried out synchrotron single-crystal X-ray diffraction measurements on a natural sample of manganese dolomite [kutnohorite, Ca1.11Mn0.89(CO3)2] in a diamond-anvil cell up to 51.2 GPa at room temperature with neon as the pressure-transmitting medium. The manganese dolomite sample remains stable in the rhombohedral structure from 1 bar to ~13.3 GPa. The equation of state of Ca1.11Mn0.89(CO3)2was determined: V0= 334.06 ± 0.29 Å3, K0= 99.9 ± 4.7 GPa, and K0′=4.3±0.9;$K_{0}^{\prime}=4.3 \pm 0.9;$when K0′$K_{0}^{\prime}$is fixed at 4.0, V0= 334.04 ± 0.24 Å3, and K0= 101.4 ± 1.5 GPa. Upon further compression at room temperature, the split and disappearance of diffraction spots were observed. That is, the rhombohedral structure of manganese dolomite becomes highly distorted to lose its long-range order at 13.3–51.2 GPa at room temperature. Moreover, our single-crystal X-ray difraction results reveal the mechanisms of the reported lattice and internal Raman mode splits of the same manganese dolomite sample approximately at 13 and 24 GPa, respectively. These results suggest manganese-bearing carbonates may play a distinct role in the deep carbon cycle.

Layered materials have attracted extensive attention due to their exceptional physical and chemical properties. Understanding the structural evolution of such materials under high pressure is crucial for the development of new functional materials. In this study, the structure evolution of the synthesized layered rare-earth hydroxyhalide YCl(OH)2under high pressures up to approximately 9.4 GPa was explored by using a diamond anvil cell combined with synchrotron single-crystal X-ray diffraction. Simultaneously, high-pressure Raman spectroscopy experiment was conducted to 10.3 GPa. Our findings indicate that YCl(OH)2maintains its symmetry within the experimental pressure range. The pressure–volume data of YCl(OH)2were fitted to the third-order Birch–Murnaghan equation of state (EoS) to derive its EoS parameters including zero-pressure unit-cell volume (VT0), isothermal bulk modulus (KT0), and its pressure derivative (K’T0): VT0= 142.47 (1) Å3, KT0= 38.2 (18) GPa, and K’T0= 9.8 (1). However, the unit-cell parameters a, b, and cexhibit a distinct compressional behavior, with the a-axis being the most compressible and the b-axis being the least. Particularly noteworthy is the observation that YCl(OH)2displays a negative linear compressibility along the b-axis within the pressure range of 0.4–5.3 GPa. Further detailed structure refinement and Raman spectroscopy analyses indicate that the anomalous behavior of the b-axis could be attributed to the formation of the O–H···O hydrogen bonding chains along the bdirection. Moreover, the coordination number of Y3+increased from 8 to 9 as the pressure reached 5.3 GPa due to the reduction of the interlayer spacing upon compression, ultimately leading to the closure of the interlayer gap.

Tephroite (Mn2SiO4), together with some manganese (Mn)-rich mineral inclusions, has been found in ophiolite-hosted diamonds, possibly originating from Mn-nodules and sediments that were once deposited on the oceanic floor and later subducted into the deep mantle, which provides evidence for oceanic crustal recycling. However, the state and behavior of tephroite under high-pressure and high-temperature conditions remain poorly understood. In this study, we conducted in situ synchrotron single-crystal X-ray difraction (XRD) and Raman spectroscopy of synthetic tephroite up to ~30 GPa and ~900 K. The XRD and Raman spectroscopy experiments in this study first show that tephroite undergoes a pressure-induced, irreversible, amorphous transformation above ~20 GPa. Temperature (<900 K) is found to be an insignificant factor governing the process of amorphous transformation. Amorphous tephroite may be a potential phase in a rapidly cooling oceanic lithospheric subduction slab stagnating at the bottom of the mantle transition zone.

Hydroxylation of wadsleyite, β-(Mg,Fe)2SiO4, is associated with divalent cation defects and well known to afect its physical properties. However, an atomic-scale understanding of the defect structure and hydrogen bonding at high pressures is needed to interpret the influence of water on the behavior of wadsleyite in the mantle transition zone. We have determined the pressure evolution of the wadsleyite crystal symmetry and structure, including all O∙∙∙O interatomic distances, up to 32 GPa using single-crystal X-ray difraction on two well-characterized, Fe-bearing (Fo90) samples containing 0.25(4) and 2.0(2) wt% H2O. Both compositions undergo a pressure-dependent monoclinic distortion from orthorhombic symmetry above 9 GPa, with the less hydrous sample showing a larger increase in distortion at increased pressures due to the diference in compressibility of the split M3 site in the monoclinic setting arising from preferred vacancy ordering at the M3B site. Although hydrogen positions cannot be modeled from the X-ray difraction data, the pressure evolution of the longer O1∙∙∙O4 distance in the structure characterizes the primary hydrogen bond length. We observe the hydrogen-bonded O1∙∙∙O4 distance shorten gradually from 3.080(1) Å at ambient pressure to about 2.90(1) Å at 25 GPa, being still much longer than is defined as strong hydrogen bonding (2.5–2.7 Å). Above 25 GPa and up to the maximum pressure of the experiment at 32.5 GPa, the hydrogen-bonded O1∙∙∙O4 distance decreases no further, despite the fact that previous spectroscopic studies have shown that the primary O-H stretching frequencies continuously drop into the regime of strong hydrogen bonding (<3200 cm–1) above ~15 GPa. We propose that the primary O1-H∙∙∙O4 hydrogen bond in wadsleyite becomes highly nonlinear at high pressures based on its deviation from frequency-distance correlations for linear hydrogen bonds. One possible explanation is that the hydrogen position shifts from being nearly on the long O1-O4 edge of the M3 site to a position more above O1 along the c-axis.

The high-pressure and high-temperature behaviors of manganotantalite Mn(Ta,Nb)2O6have been investigated by single-crystal X-ray diffraction and Raman spectroscopy combined with diamond anvil cell technique, as well as first-principle calculations. A pressure-induced reversible phase transition of manganotantalite occurs at 9.5 GPa and room temperature, accompanied by a large volume collapse (∼7.0%) and drastic color change from brownish-yellow to red. The space groups of low-pressure (LP) and high-pressure (HP) phases are the same (Pbcn), but the coordination numbers of Mn increase from six to eight and Ta increase from six to seven, respectively. The band gap becomes narrow from 2.37 to 1.59 eV. We determined the P-Tphase diagram of manganotantalite with a positive Clapeyron slope of dP/dT= 0.0073 GPa/K. The P-Vdata were fitted to a second-order Birch–Murnaghan equation of state with B0= 149(4) GPa for the LP phase and B0= 188(3) GPa for the HP phase. The isothermal Grüneisen parameters were determined to be 0.23∼2.03 of the LP phase and 0.59∼0.86 of the HP phase for Raman modes. High-pressure behaviors of Mn(Ta,Nb)2O6indicate that this kind of material is a potential effective pressure sensor to monitor pressure change or warn pressure abnormality.

Olivine is the most abundant mineral in the Earth’s upper mantle and subducting slabs. Studying the structural evolution and equation of state of olivine at high-pressure is of fundamental importance in constraining the composition and structure of these regions. Hydrogen can be incorporated into olivine and significantly influence its physical and chemical properties. Previous infrared and Raman spectroscopic studies indicated that local structural changes occur in Mg-rich hydrous olivine (Fo ≥ 95; 4883–9000 ppmw water) at high-pressure. Since water contents of natural olivine are commonly <1000 ppmw, it is inevitable to investigate the effects of such water contents on the equation of state (EoS) and structure of olivine at high-pressure. Here we synthesized a low water content hydrous olivine (Fo95; 1538 ppmw water) at low SiO2activity and identified that the incorporated hydrogens are predominantly associated with the Si sites. We performed high-pressure single-crystal X‑ray diffraction experiments on this olivine to 29.9 GPa. A third-order Birch-Murnaghan equation of state (BM3 EoS) was fit to the pressure-volume data, yielding the following EoS parameters: VT0= 290.182(1) Å3, KT0= 130.8(9) GPa, and KT0′=4.16(8).$K_{\mathrm{T} 0}^{\prime}=4.16(8).$The KT0is consistent with those of anhydrous Mg-rich olivine, which indicates that such low water content has negligible effects on the bulk modulus of olivine. Furthermore, we carried out the structural refinement of this hydrous olivine as a function of pressure to 29.9 GPa. The results indicate that, similar to the anhydrous olivine, the compression of the M1-O and M2-O bonds are comparable, which are larger than that of the Si-O bonds. The compression of M1-O and M2-O bonds of this hydrous olivine are comparable with those of anhydrous olivine, while the Si-O1 and Si-O2 bonds in the hydrous olivine are more compressible than those in the anhydrous olivine. Therefore, this study suggests that low water content has negligible effects on the EoS of olivine, though the incorporation of water softens the Si-O1 and Si-O2 bond.

We report pressure-induced superconductivity in a ternary and nonmagnetic Cu-containing semiconductor, Cu2Br2Se6, with a wide band gap of 1.89 eV, in which the Cu and Br atoms generate infinite 21helical chains along the c-axis and are linked by the cyclohexane-like Se6rings to form a three-dimensional framework. We find that this framework is remarkably robust under compression, and the ambient-pressure phase survives at least to our experimental limit of 32.1 GPa. Concurrent semiconductor-to-metal transition and superconductivity are observed above 21.0 GPa. The superconducting temperature monotonically increases from 4.0 to 6.7 K at 40.0 GPa. First-principles calculations show that the emergence of superconductivity is associated with the formation of weak multicentered bonds that involve the increase in coordination of the Cu atoms and a subset of the Se atoms. The observation of superconductivity in this type of nonmagnetic transition-metal-based material will inspire the exploration of related new superconductors under pressure.

Diopside is one of the most important end-members of clinopyroxene, which is an abundant mineral in upper-mantle petrologic models. The amount of clinopyroxene in upper-mantle pyrolite can be ∼15 vol%, while pyroxenite can contain as high as ∼60 vol% clinopyroxene. Knowing the elastic properties of the upper-mantle diopside at high pressure-temperature conditions is essential for constraining the chemical composition and interpreting seismic observations of region. Here we have measured the single-crystal elasticity of Fe-enriched diopside (Di80Hd20, Di-diopside, and Hd-hedenbergite; also called Fe-enriched clinopyroxene) at high-pressure conditions up to 18.5 GPa by using in situ Brillouin light-scattering spectroscopy (BLS) and synchrotron X-ray diffraction in a diamond-anvil cell. Our experimental results were used in evaluating the effects of pressure and Fe substitution on the full single-crystal elastic moduli across the Di-Hd solid-solution series to better understand the seismic velocity profiles of the upper mantle. Using the third- or fourth-order Eulerian finite-strain equations of state to model the elasticity data, the derived aggregate adiabatic bulk and shear moduli (KS0, G0) at ambient conditions were determined to be 117(2) and 70(1) GPa, respectively. The first- and second-pressure derivatives of bulk and shear moduli at 300 K were (∂KS/∂P)T= 5.0(2), (∂2KS/∂P2)T= –0.12(4) GPa−1and (∂G/∂P)T= 1.72(9), (∂2G/∂P2)T= –0.05(2) GPa−1, respectively. A comparison of our results with previous studies on end-member diopside and hedenbergite in the literatures shows systematic linear correlations between the Fe composition and single-crystal elastic moduli. An addition of 20 mol% Fe in diopside increases KS0by ∼1.7% (∼2 GPa) and reduces G0by ∼4.1% (∼3 GPa), but has a negligible effect on the pressure derivatives of the bulk and shear moduli within experimental uncertainties. In addition, our modeling results show that substitution of 20 mol% Fe in diopside can reduce VPand VSby ∼1.8% and ∼3.5%, respectively, along both an expected normal mantle geotherm and a representative cold subducted slab geotherm. Furthermore, the modeling results show that the VPand VSprofiles of Fe-enriched pyroxenite along the cold subducted slab geotherm are ∼3.2% and ∼2.5% lower than AK135 model at 400 km depth, respectively. Finally, we propose that the presence of Fe-enriched pyroxenite (including Fe-enriched clinopyroxene, Fe-enriched orthopyroxene, and Feenriched olivine), can be an effective mechanism to cause low-velocity anomalies in the upper mantle regions atop the 410 km discontinuity at cold subudcted slab conditions.

Jeffbenite (Mg3Al2Si3O12) is a tetragonal phase found in so far only in superdeep diamonds, and its thermoelastic parameters are a prerequisite for determining entrapment pressures as it is regarded as a potential indicator for superdeep diamonds. In this study, the thermoelastic properties of synthetic Fe3+‐jeffbenite were measured up to 33.7 GPa and 750 K. High‐temperature static compression data were fitted, giving (∂KT0/∂T)P= −0.0107 (4) GPa/K and αT= 3.50 (3) × 10−5K−1. The thermoelastic properties and phase stability are applied to modeling isomekes, or P‐Tpaths intersecting possible conditions of entrapment in diamond. We calculate that under ideal exhumation, jeffbenite entrapped at mantle transition zone conditions will exhibit a high remnant pressure at 300 K (Pinc) of ∼5.0 GPa. Elastic geobarometry on future finds of jeffbenite inclusions can use the new equation of state to estimate entrapment pressures for this phase with still highly uncertain stability field in the mantle. Ongoing superdeep diamonds research is providing new insights into the Earth's deep mantle. Natural superdeep diamonds and its inclusions can show compelling evidence for retrograde conversion from the lower mantle or transition zone precursors; along with carbonate melt‐peridotite reactions. Jeffbenite with a composition of Mg3Al2Si3O12, found in so far only in superdeep diamonds can be regarded as a potential indicator mineral for superdeep diamonds. Recent synthesis of Fe3+‐rich jeffbenite provides an opportunity for in‐situ measurements to study the thermodynamic properties of jeffbenite at deep‐mantle conditions. Thus, in this study, we explored the high pressure and temperature stability and thermoelastic properties of Fe‐bearing jeffbenite up to 33.7 GPa and 750 K. The thermoelastic data and phase stability were measured and the results are applied to modeling the isomekes, or P‐Tpaths intersecting possible conditions of entrapment and along which the pressure on the inclusion is equal to the external pressure on the diamond host. Our finding can be applied to determining entrapment pressures in such diamond inclusions in future finds and its primary or retrograde history is essential in understanding mantle dynamics and the hidden consequences of plate tectonics. We measure the phase stability and thermoelastic properties on synthetic Fe‐bearing jeffbeniteThe thermoelastic data are applied to modeling isomekes and the remnant pressure (Pinc) is determinedThe smaller thermal expansivity of jeffbenite gives rise to a broader pressure and temperature stability field in the upper lower mantle We measure the phase stability and thermoelastic properties on synthetic Fe‐bearing jeffbenite The thermoelastic data are applied to modeling isomekes and the remnant pressure (Pinc) is determined The smaller thermal expansivity of jeffbenite gives rise to a broader pressure and temperature stability field in the upper lower mantle

The elasticity of single-crystal hydrous pyrope with ~900 ppmw H2O has been derived from sound velocity and density measurements using in situ Brillouin light spectroscopy (BLS) and synchrotron X‑ray diffraction (XRD) in the diamond-anvil cell (DAC) up to 18.6 GPa at room temperature and up to 700 K at ambient pressure. These experimental results are used to evaluate the effect of hydration on the single-crystal elasticity of pyrope at high pressure and high temperature (P-T) conditions to better understand its velocity profiles and anisotropies in the upper mantle. Analysis of the results shows that all of the elastic moduli increase almost linearly with increasing pressure at room temperature, and decrease linearly with increasing temperature at ambient pressure. At ambient conditions, the aggregate adiabatic bulk and shear moduli (KS0, G0) are 168.6(4) and 92.0(3) GPa, respectively. Compared to anhydrous pyrope, the presence of ~900 ppmw H2O in pyrope does not significantly affect its KS0and G0within their uncertainties. Using the third-order Eulerian finite-strain equation to model the elasticity data, the pressure derivatives of the bulk [(∂KS/∂P)T] and shear moduli [(∂G/∂P)T] at 300 K are derived as 4.6(1) and 1.3(1), respectively. Compared to previous BLS results of anhydrous pyrope, an addition of ~900 ppmw H2O in pyrope slightly increases the (∂KS/∂P)T, but has a negligible effect on the (∂G/∂P)Twithin their uncertainties. The temperature derivatives of the bulk and shear moduli at ambient pressure are (∂KS/∂T)P= –0.015(1) GPa/K and (∂G/∂T)P= –0.008(1) GPa/K, which are similar to those of anhydrous pyrope in previous BLS studies within their uncertainties. Meanwhile, our results also indicate that hydrous pyrope remains almost elastically isotropic at relevant high P-Tconditions, and may have no significant contribution to seismic anisotropy in the upper mantle. In addition, we evaluated the seismic velocities (vPand vS) and the vP/vSratio of hydrous pyrope along the upper mantle geotherm and a cold subducted slabs geotherm. It displays that hydrogen also has no significant effect on the seismic velocities and the vP/vSratio of pyrope at the upper mantle conditions.

We carried out three series of amphibole crystallization experiments from hydrous basaltic melt to calibrate the dependence of crystal growth rate on temperature and pressure in amphibole-bearing igneous rocks. One series of 100 h duration multi-anvil experiments were carried out at a constant pressure of 0.6 GPa and variable temperatures from 860 to 970 °C. The second series was conducted at a constant temperature of 970 °C and variable pressures from 0.6 to 2.6 GPa. The third series examined the time dependence at 970 °C and 0.6 GPa, with durations from 1 to 100 h. A verification experiment showing both reproducibility and the ability of these three series to predict behavior at novel conditions was performed in a piston cylinder at 1.0 GPa and 900 °C for 63 h. All experiments yielded mostly amphibole in a quenched glass of granitic to granodioritic composition. We used the two-dimensional thin section method to measure the crystal size distribution (CSD) of amphibole in the experimental products. Concave-down CSD curves at small sizes indicate a textural coarsening process during the crystallization. The CSD data were inverted using canonical CSD theory for CSD growth rate; maximum and average growth rates of amphibole were also inferred directly from the maximum and average grain size and crystallization time. The maximum growth rate is, of course, always larger than the average growth rate, which is in turn slightly larger than the CSD growth rate, suggesting that CSD growth rate is an adequate measure of the average growth rate of a mineral in magmatic rocks. The CSD growth rate increases with increasing temperature in the isobaric series and with increasing pressure at constant temperature. However, the growth rate is negatively correlated with crystallization time at constant temperature and pressure. Based on the experimental results, a functional form for evaluating growth rate at known pressure and temperature from an observed amphibole CSD was developed and applied to a diorite collected from the eastern Tianshan Mountains, Xinjiang Uygur autonomous region, NW China. The estimated growth rate of amphibole is between 1.6 × 10–9mm/s and 5.6 × 10–7mm/s, and combined with petrological constraints on pressure and temperature, the corresponding crystallization time was between 0.1 and 4.3 yr in the natural diorite.

Nickel is an abundant element in the bulk earth, and nickel-dominant olivine, liebenbergite, is the only igneous nickel-rich silicate found in nature. In this study, we used high-pressure single-crystal diffraction to explore the compressional behavior of a synthetic liebenbergite sample up to 42.6 GPa at ambient temperature. Over the studied pressure range, the liebenbergite sample retains the orthorhombic Pbnmstructure, and no phase transition is observed. A third-order Birch-Murnaghan equation of state was used to fit the pressure behavior of the unit-cell volume, lattice parameters, the polyhedral volume, and the average bond length within each polyhedron. The best-fit bulk modulus KT0= 163(3) GPa and its pressure derivative KT0′$\begin{array}{} K_{{\rm T}0}' \end{array} $= 4.5(3). We find that liebenbergite is the most incompressible olivine-group silicate reported thus far, and Ni2+tends to increase the isothermal bulk modulus of both olivine- and spinel-structured silicates. Consequently, Ni-rich olivine has a higher density compared to Ni-poor olivine at the upper mantle P-Tconditions; however enrichment of Ni in mantle olivine is generally too low to make this density difference relevant for fractionation or buoyancy.

Synchrotron‐based high‐pressure/high‐temperature single‐crystal X‐ray diffraction experiments to ~24 GPa and 700 K were conducted on eclogitic garnets (low‐Fe: Prp28Alm38Grs33Sps1and high‐Fe: Prp14Alm62Grs19Adr3Sps2) and omphacites (low‐Fe: Quad57Jd42Ae1and high‐Fe: Quad53Jd27Ae20), using an externally heated diamond anvil cell. Fitting the pressure‐volume‐temperature data to a third‐order Birch‐Murnaghan equation of state yields the thermoelastic parameters including bulk modulus (KT0), its pressure derivative (K′T0), temperature derivative ((∂KT/∂T)P), and thermal expansion coefficient (αT). The densities of the high‐Fe and low‐Fe eclogites were then modeled along typical geotherms of the normal mantle and the subducted oceanic crust to the transition zone depth (550 km). The metastable low‐Fe eclogite could be a reason for the stagnant slabs within the upper range of the transition zone. Eclogite would be responsible for density anomalies within 100–200 km in the upper mantle of Asia. Eclogite mainly consists of pyrope‐almandine‐grossular garnet and sodium‐rich pyroxene (omphacite) and is a key component of the Earth's upper mantle and oceanic crust. It plays an important role in the mantle convection. The lack of thermoelastic parameters of eclogitic garnets and omphacites hampers accurate modeling of eclogite density at deep‐Earth pressure‐temperature conditions. In this study, we obtained the thermoelastic parameters of natural eclogitic garnets and omphacites and then modeled the densities of high‐Fe and low‐Fe eclogites in the subducted oceanic crust and the normal upper mantle. In the upper mantle, eclogite enhances the slab subduction into the transition zone; however, the presence of the metastable low‐Fe eclogite would promote the slab stagnation within the upper range of the transition zone. Additionally, eclogite can explain positive density anomalies at depths of 100–200 km of the upper mantle of Asia identified by seismic observations. Single‐crystal X‐ray diffraction experiments were carried out on high‐Fe and low‐Fe eclogitic garnets and omphacites to 24 GPa and 700 KMetastable low‐Fe eclogite may contribute to the slab stagnation in the upper range of the transition zoneEclogite can explain density anomalies at depths of 100–200 km in the upper mantle of Asia

Synchrotron‐based high‐pressure and temperature single‐crystal X‐ray diffraction experiments were conducted on two hydrous orthoenstatite samples (oEn#1: Mg1.004Si0.996O3, ~619 ppm water; oEn#2: Mg0.947Ni0.055Si0.998O3, ~696 ppm water) to ~34 GPa and 700 K, using resistively heated diamond anvil cells. The α‐opx (Pbcaspace group)→β‐opx (P21/cspace group) phase transition of oEn#1 occurs at 12.90(2) GPa, and the β‐opx phase persists to 34.25(1) GPa. The α‐βtransition of oEn#2 occurs at 13.50(1) GPa, and a new isosymmetric β‐opx→β‐opxII transition takes place at 29.80(4) GPa. The β‐opxII phase is preserved down to 24.53(3) GPa during decompression. The transition to the monoclinic β‐opxII phase is interpreted as a result of incorporation of Ni2+into the orthoenstatite structure. Fitting the third‐order Birch‐Murnaghan thermal equation of state to the single‐crystal P‐V‐T data yields the thermoelastic parameters of the α‐ and β‐opx phases for both orthoenstatite samples. This study is the first attempt to determine the thermal equation of state of the β‐opx phase. Our results suggest that several hundred ppm of water has negligible effects on the bulk modulus of orthoenstatite but notably enhances the thermal expansion. The potential effects of metastable orthoenstatite on subduction zone dynamics are discussed, and the possible contributions of displacive phase transitions to enhancement of the transformational faulting mechanism of the deep‐focus earthquakes in subducted slabs are considered. The presence of metastable orthoenstatite within cold slabs could promote slab stagnation above the 660‐km discontinuity. Single‐crystal X‐ray diffraction experiments are carried out on hydrous Mg end‐member and Ni‐bearing orthoenstatite(oEn) to 30 GPa and 700 KSeveral hundred ppm of water has negligible effects on the phase transition and bulk modulus of oEn but promotes the thermal expansionNi2+strongly influences the phase transition of oEn and causes a different high‐pressure transition (β‐opx→β‐opxII) than that in Fe‐oEn

(Ca, Mg)-rich clinopyroxenes are abundant in Earth’s upper mantle and subduction zones. Experimental studies on the thermoelastic properties of these minerals at simultaneous high pressure and high temperature are important for constraining of the composition and structure of the Earth. Here, we present a synchrotron-based single-crystal X-ray diffraction study of natural diopside-dominated augite [(Ca0.89Na0.05Mg0.06)(Mg0.74Fe0.11Al0.14Ti0.01)(Si1.88Al0.12) O6.00] at Pand Tto ~27 GPa and 700 K. The experiment simulates conditions in cold subducting slabs, and results indicate that augite is stable over this pressure and temperature range. A third-order high-temperature Birch-Murnaghan equation was fit with the pressure-volume-temperature data, yielding the following thermoelastic parameters: KT0= 111(1) GPa, KT0′$K_{\text T0}'$ = 4.1(1), (∂K0/∂T)P= −0.008(5) GPa/K and αT= 4(1)×10−5K−1+2(3)×10−8K−2T. A strain analysis shows that the compression along the three principal stress directions is highly anisotropic with ε1:ε2:ε3 = 1.98:2.43:1.00. Additionally, high-pressure structural refinements of room-temperature polyhedral geometry, bond lengths and O3-O3-O3 angle were investigated to ~27 GPa at ambient temperature. Pressure dependences of polyhedral volumes and distortion indicate that the substitution of Al3+for Si4+significantly changes the compressional behavior of the TO4-tetrahedron in augite. Density calculations of this augite along a subducting slab geotherm suggest that augite as well as other common clinopyroxenes would promote slab stagnations at transition zone depths if they are metastably preserved in significant quantities.

Pyroxenes are among the most important minerals of Earth's crust and upper mantle and play significant role in controlling subduction at convergent margins. In this study, synchrotron‐based single‐crystal X‐ray diffraction experiments were carried out on a natural aegirine [NaFe3+Si2O6] sample at ambient temperature and high pressures to 60 GPa, simulating conditions within the coldest part of a subduction zone consisting of old lithosphere. The diffraction data reveal no obvious sign of structural phase transition in aegirine within this pressure range; however, several relevant structural parameter trends change noticeably at approximately 24 GPa, indicating the presence of the previously predicted isosymmetric bonding change, related to increase of coordination number of Na+at M2 site. The pressure‐volume data, fit with third‐order Birch‐Murnaghan (BM3) equation of state over the whole pressure range, yields KT0= 126(2) GPa and K′T0= 3.3(1), while separate BM3 fits performed for the 0–24.0 GPa and 29.9–60.4 GPa pressure ranges give KT0= 118(3) GPa, K′T0= 4.2(3) and KT0= 133(2) GPa, K′T0= 3.0(1), suggesting that the structure stiffens as a result of the new bond formation. Aegirine exhibits strong anisotropic compression with unit strain axial ratios ε1:ε2:ε3= 1.00:2.44:1.64. Structural refinements reveal that NaO8polyhedron is the most compressible and SiO4tetrahedron has the lowest compressibility. The consequence of bonding transition is that the compressional behavior of aegirine below ~24 GPa and above that pressure is quite different, with likely consequences for relevant thermodynamic parameters and ion diffusion coefficients. Single‐crystal X‐ray diffraction experiments are carried out on aegirine [NaFe3+Si2O6] at ambient temperature and high pressures to 60 GPaA second‐order isosymmetric phase transition is detected and characterized by a discontinuity of bulk modulusIf such clinopyroxenes can be preserved in cold subducted slab, the isosymmetric phase transition would cause an increase in buoyancy

The pressure-volume-temperature (P-V-T) equation of state (EoS) of synthetic uvarovite has been measured at high temperatures up to 900 K and high pressures up to 16.20 GPa, by using in situ angle-dispersive X-ray diffraction and diamond-anvil cell. Analysis of room-temperature P-V data to a third-order Birch-Murnaghan EoS yielded: V0= 1736.9 ± 0.5 Å3, K0= 162 ± 2 GPa, and K′0= 4.5 ± 0.3. With K′0fixed to 4.0, we obtained: V0= 1736.5 ± 0.3 Å3and K0= 164 ± 1 GPa. Fitting of our PV- T data by means of the high-temperature third-order Birch-Murnaghan equations of state, given the thermoelastic parameters: V0= 1736.8 ± 0.8 Å3, K0= 162 ± 3 GPa, K′0= 4.3 ± 0.4, (∂K/∂T)P = -0.021 ± 0.004 GPa/K, and α0= (2.72 ± 0.14)×10-5K-1. We compared our elastic parameters to the results from the previous studies for uvarovite. From the comparison of these fittings, we propose to constrain the bulk modulus and its pressure derivative to K0= 162 GPa and K′0= 4.0-4.5 for uvarovite. Present results were also compared with previous studies for other ugrandite garnets, grossular and andradite, which indicated that the compression mechanism of uvarovite might be similar with grossular and andradite. Furthermore, a systematic relationship, K0(GPa) = 398.1(7)-0.136(8) V0(Å3) with a correlation coefficient R2of 0.9999, has been established based on these isostructural analogs. Combining these results with previous studies for pyralspite garnets-pyrope, almandine, and spessartine-the compositional dependence of the thermoelastic parameters (bulk modulus, thermal expansion, and the temperature derivative of the bulk modulus) were discussed.

The phase transitions of natural San Carlos Fe‐, Al‐ and Ca‐bearing orthopyroxene and two synthetic orthopyroxenes containing Al (up to 12 wt. % Al2O3) and Fe (up to 15 wt. % FeO) were investigated at high pressures and temperatures up to ∼30 GPa and 700 K using synchrotron‐based single‐crystal X‐ray diffraction. These orthopyroxenes undergo α‐opx → β‐opx → γ‐opx phase transitions with increasing pressure and temperature. We quantitatively described how the composition influences the pressures of the phase transitions. The results indicated that the variations in Mg, Fe, and Al contents do not significantly influence the pressure of the α‐opx → β‐opx transition (Pα‐β). For the β‐opx → γ‐opx phase transition, increasing Fe content decreases the Pβ‐γwhile increasing Al content increases the Pβ‐γ. The incorporation of Ca increases the Pα‐βand decreases the Pβ‐γ. The thermal equations of states of α‐opx and β‐opx for these three orthopyroxenes were determined using the unit‐cell volume collected at high pressures and temperatures, which have been used to establish a density model to interpret the cold stagnant slabs. Our experimental results have indicated that β‐opx and γ‐opx are possible metastable phases of natural orthopyroxenes within cold stagnant slabs in the mantle transition zone. Orthopyroxene ((Mg, Fe, Ca)(Mg, Fe, Al)(Si, Al)2O6) is a major rock‐forming mineral in subducting slabs, and its metastable phases are considered to be related to the stagnation of slabs which are located at the transition zone due to its low density in comparison to other major slab minerals. Studies on the phase transitions of orthopyroxenes under the pressure‐temperature conditions of subducting slabs are necessary to understand the metastable phases of orthopyroxenes within stagnant slabs. Here, for the first time, we investigated the phase transitions of natural and synthetic orthopyroxenes in a large range of compositional variations under the pressure‐temperature conditions present in extremely cold subducting slabs up to the bottom of Earth's transition zone. The results indicated that the α‐opx → β‐opx → γ‐opx phase transitions could occur for natural orthopyroxenes under such pressure‐temperature conditions. Therefore, the β‐opx and γ‐opx are possible metastable phases of orthopyroxenes within stagnant slabs in the transition zone. Using the obtained thermal equation of state of orthopyroxene and its high‐pressure phases together with literature results, we modeled the densities of cold subducting slab which includes metastable orthopyroxene and olivine. We show that the existence of metastable orthopyroxene and olivine could result in slab stagnation within the upper range of the transition zone. Single‐crystal X‐ray diffraction experiments were carried out on Fe‐, Al‐ and Ca‐bearing orthopyroxenes under high P‐TconditionsCompositional and temperature effects on the phase transitions and equations of state of orthopyroxenes were investigatedβ‐opx and γ‐opx are possible metastable phases of natural orthopyroxenes within cold stagnant slabs Single‐crystal X‐ray diffraction experiments were carried out on Fe‐, Al‐ and Ca‐bearing orthopyroxenes under high P‐Tconditions Compositional and temperature effects on the phase transitions and equations of state of orthopyroxenes were investigated β‐opx and γ‐opx are possible metastable phases of natural orthopyroxenes within cold stagnant slabs

(Mg, Fe)SiO3orthopyroxene is an abundant mineral of oceanic subducting slabs. In‐situ high‐pressure and high‐temperature single‐crystal X‐ray diffraction has been used to investigate the phase transition of orthopyroxene across the enstatite‐ferrosilite (En‐Fs) join (En70Fs30, En55Fs45, En44Fs56and Fs100) up to 24.3 GPa and 800 K, simulating conditions within the coldest part of a subduction zone consisting of an old and rapidly subducting slab. Instead of the orthopyroxene → high‐pressure clinopyroxene transition, the α‐opx → β‐opx and β‐opx → γ‐opx phase transition are observed at 7.2–15.3 and 11.6–21.1 GPa (depending on the Fs content), respectively. This study indicates that the pressure‐induced phase transition of (Mg, Fe)SiO3orthopyroxene under relatively low temperature (<800 K) could be different than those occurring under relatively high temperature (>800 K). Additionally, the α‐opx → β‐opx → γ‐opx phase transition could exist within the center of the extremely cold slabs (like Tonga), where such low temperature persists to ~600‐km depth. (Mg, Fe)SiO3is the most abundant chemical compound in Earth's mantle. Investigating its phase relations at high‐pressure and high‐temperature is of fundamental importance in constraining the composition and understanding the structure of the Earth's interior. Previous studies have well established the phase diagram of (Mg, Fe)SiO3at high pressure and high temperature. Orthopyroxene is a low‐pressure phase; with increasing pressure and temperature, orthopyroxene transforms to the high‐pressure clinopyroxene, then, it transforms to akimotoite or decomposes to wadsleyite + stishovite. These phase transitions require temperatures higher than 900 K, which are easily satisfied in the normal mantle or relatively warm subduction zone conditions. However, extremely low‐temperature region exists in the center of some old and rapidly subducting slabs (e.g., Tonga), and such low‐temperature region (~800 K) can extend to ~600‐km depth. In this study, we investigate the phase relations of (Mg, Fe)SiO3orthopyroxene with several different compositions to 24.3 GPa and 800 K. A different phase transition path is observed, that is, the α‐opx → β‐opx → γ‐opx at pressures within the transition zone depths. Therefore, the result of this study adds one more piece of information to our understanding of phase relations of (Mg, Fe)SiO3orthopyroxene within the extremely cold subducted slabs. Phase transition of MgSiO3‐FeSiO3solid solutions was investigated to 24.3 GPa and 800 K using single‐crystal X‐ray diffractionMetastable orthopyroxene progressively transforms into the β‐opx and γ‐opx phase at high temperature (800 K) and high pressureMetastable orthopyroxene and its high‐pressure phases could exist within the coldest part of old slabs and contribute to slab stagnation

Endometrial cancer (EC) is one of the most common cancers among women worldwide. Kinesin family member C1 (KIFC1) has been demonstrated to play crucial roles in various tumors. However, the function of KIFC1 in EC remains to be revealed. In this study, upregulation of KIFC1 expression in human EC tissues was found from analysis on data from The Cancer Genome Atlas (TCGA), and positively correlated with short survival outcome of EC patients. In addition, the mRNA and protein levels of KIFC1 were confirmed to be up-regulated in EC cells (Ishikawa, HEC-1B, HEC-1A and KLE) compared to human normal endometrial stromal cells (hESCs) by quantitative real time PCR and western blot. In vitrofunctional experiments showed that overexpression of KIFC1 promoted proliferation, migration and invasion of EC cells, while KIFC1 depletion showed the opposite results. Moreover, KIFC1 knockdown suppressed tumor growth in mice. Further mechanism analysis showed that KIFC1 participated in the regulation of EC progression through regulating the PI3K/AKT signaling pathway. Collectively, KIFC1 promoted proliferation and invasion through modulating PI3K/AKT signaling pathway in EC, implying that KIFC1 might provide a promising therapeutic target for the therapy of EC.